Optical-dispersion is a well-known optical phenomenon which refers to wavelength dependency of refractive index in media. For applications such as spectroscopy, optical-dispersion can be desirable to cause wavelength separation. For imaging optics, optical-dispersion causes undesirable wavelength dependent focal shift, called chromatic aberration. A variety of solutions to reduce chromatic aberration are known in the art.
An achromatic lens provides chromatic aberration compensation by utilizing different glass types with different optical-dispersion, often crown glass and flint glass. One example of an achromatic lens is a doublet-lens. A doublet-lens consists of a positive-lens and a negative-lens, with different optical-dispersion, sandwiched together, forming a single optic. In the doublet-lens, the different optical-dispersion and lens shape reduce chromatic aberration, generally limited for focal shift correction of two wavelengths. Increased wavelength correction can be accomplished with additional lenses, air-space between lenses, and aspheric lens shape. Another correction solution utilizes gradient refractive index (GRIN) films.
One method to correct chromatic aberration with GRIN optics is by forming a lens out of a continuous GRIN material. One such method is described in U.S. Patent Publication No. US 20130003186 A1, where wavelength separation, caused by initial dispersion of light entering into a single-lens, is partially corrected by the optical-dispersion of a continuous GRIN material that form the lens.
This application relates to another approach.